This disclosure relates generally to a method of determining the concentration of a substance using radiolabeled materials and specifically to a method of determining the concentration of thyroxine binding globulin in a fluid sample using radiolabeled thyroxine (T.sub.4) and immobilized anti-TBG antibodies.
The diagnosis of dysfunction of the thyroid gland and related organs and systems is greatly facilitated by the rapid and accurate assay of various serum hormones such as triiodothyronine (T.sub.3), thyroxine (T.sub.4), thyroxine stimulating hormone (TSH) and certain globulins such as thyroxine binding globulin (TBG). Various methods of assaying such constituents are well known. Present systems for the assay of TBG in human serum, however, are non-quantitative (i.e. T.sub.3 uptake test) or consist of classical RIA procedures having attendent disadvantages (i.e. intrinsically labeled antigens).
Quite surprisingly, it has been found that by modifying certain radioassay techniques and using such modifications with a novel reagent consisting of immobilized anti-TBG antibodies, a relatively quick and simple method of determining TBG concentrations is possible. Details of the method are described herein.